Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides1,2,3,4. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface5,6,7 to reveal a remarkably complex evolution of electron–phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface8,9,10,11,12,13, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron–phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.
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We thank A. Fête, M. Grilli, L. Patthey, V. Strocov, J.-M. Triscone, D. van der Marel and Z. Zhong for discussions. The ARPES work was supported by the Swiss National Science Foundation (200021-146995). The spectral function calculations were supported at SLAC and Stanford University by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515, and by the Computational Materials and Chemical Sciences Network (CMCSN), under Contract No. DE-SC0007091. A portion of the computational work was performed using the resources of the National Energy Research Scientific Computing Center supported by the US Department of Energy, Office of Science, under Contract No. DE-AC02-05CH11231. M.S. acknowledges financial support by the Sino-Swiss Science and Technology Cooperation (No. IZLCZ2138954), J.S.-B. by the Impuls- und Vernetzungsfonds der Helmholtz Gemeinschaft (Grant No. HRJRG-408), P.D.C.K. by the UK-EPSRC (EP/I031014/1) and the Royal Society, U.D. by the ERC Advanced Grant ‘OxideSurfaces’ and W.M. by the Thailand Research Fund (TRF) under the TRF Senior Research Scholar, Grant No. RTA5680008. We acknowledge Diamond Light Source for time on beamline I05 under proposal SI11741.
The authors declare no competing financial interests.
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Wang, Z., McKeown Walker, S., Tamai, A. et al. Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid. Nature Mater 15, 835–839 (2016) doi:10.1038/nmat4623
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